Infusion device with optical sensor

ABSTRACT

An infusion device with a disposable administration set which is inexpensive to manufacture. In the preferred embodiment of the present invention the disposable administration set has a plurality of elongated cam followers connected to a plate assembly, wherein the cam followers are displace in a predetermined sequence and forced against a delivery tube by cam means driven by rotary drive means. The device also includes an optical occlusion sensor which is synchronized to operate in phase with the movement of the cam followers to measure pressure within the delivery tube at one pump phase, thereby sensing downstream occlusions, and to measure vacuum within the delivery tube at a second pump phase, thereby sensing upstream occlusions. The occlusion sensor is optical, and measures the degree of total internal reflection at the interface of the tube and the plate assembly, occlusion in the tubing.

This is a continuation of application Ser. No. 08/686,757 filed on Jul.25, 1996, "Infusion Device with Disposable Elements" to Davis et al. nowhaving U.S. Pat. No. 5,853,386.

BACKGROUND OF THE INVENTION

1. General Background

This invention relates generally to a medication infusion device foradministering fluid to patients and more particularly to an improved,ambulatory infusion device with a disposable administration set which isinexpensive to manufacture, convenient to operate and which ensues fluiddelivery at a consistent and uniform rate. More specifically, thisinvention relates to an occlusion detection system for sensing ablockage in either a supply tube which provides medication to such anambulatory infusion device or an outlet tube which provides medicationfrom such an infusion device to a patient.

2. Description of the Prior Art

As a result of the ongoing need for improved health care, there is acontinuous effort to improve the administration of intravenous fluid topatients. As is well known, medication dispensers and infusion devicesare used for infusion of predetermined amounts of medication into thebody of a patient. Various types of medication dispensers employingdifferent techniques for a variety of applications are known to exist.

In many cases it is of critical importance to provide preciselycontrolled and consistent flow rates of intravenous fluid to patients.This need for more controlled IV flow rates is only partially fulfilledby prior art displacement pumps. Specifically, particularly when suchpumps are intended for ambulatory use by a patient beyond the vicinityof a hospital or other health care facility, the occurrence of anocclusion in the pump's medication supply tube or output tube mayendanger the patient without warning. If, for example, the supplyreservoir is empty, or the supply tube becomes kinked, pinched orotherwise blocked, the supply of medication to the patient will cease.As the continued supply of some medications is necessary to sustain thepatient or remedy the patient's condition, cessation of supply may evenbe life threatening. Yet, with most ambulatory pumps, such an occlusionwould go unnoticed unless the patient is extraordinarily vigilant.

Similarly, if the needle or catheter which supplies the pump's output tothe patient becomes blocked, or the outlet tubing from the pump becomeskinked or blocked, flow of medication to the patient will cease.Furthermore, with such blockage, it may be possible for dangerously highpressures to build within the outlet tube. As this tube is resilient, itmay expand with the increased pressure, storing a significant volume ofmedication. If the rising pressure finally overcomes the blockage, thestored, pressurized medication may be supplied in a surge to thepatient, overdosing and possibly endangering the patient.

As is well known, disposable equipment for medical applications isdesirable so as to maintain a germ-free environment to prevent thetransfer of infection especially where cost prohibits cleaning andsterilization after each use. Disposable elements, especially in anambulatory infusion environment, must be low in cost, since clinicalapplication of disposable administration sets requires that theadministration sets be regularly replaced. Typically, such sets arereplaced every 24 to 48 hours, and seldom remain in use longer than oneweek. This frequent replacement interval should ideally be fulfilled byan inexpensively molded, disposable, mechanism which would normally notlast the years of service life expected from the pump itself. To bepractical, an occlusion detection system must be able to reliablyoperate with such disposable administration sets. In the prior art,occlusion sensors have typically mechanically sensed the tubing of theadministration set. Thus, such systems required a highly precise,repeatable positioning of the occlusion sensor against each newadministration set. This requirement subjected prior art sensors tofrequent failure and maintenance problems.

Furthermore, it is desirable to have a disposable administration setwhich is easy to load and unload to minimize operator errors. Thesefactors can be very important in a clinical situation when a few extraseconds may be critical to a patient's life. Typically, prior artdevices require several steps to accomplish the task of loading andunloading, particularly where a tube sensor must be placed against theadministration set to detect occlusions.

Some prior art devices incorporate a pressure transducer and diaphragmassembly to monitor fluid pressure as an indication of occlusion. Suchan occlusion detection technique is undesirable in view of thecomplexities and cost involved.

Still other prior art devices use strain gages to measure the diameterof the supply tube as a means of sensing occlusions. For example, it isknown to sense the diameter of a supply tube with a strain gage todetect upstream or supply occlusions. Thus, upon the occurrence of anocclusions in the supply tube, or an empty supply bag or vessel, avacuum will be drawn in the supply tube by the continued operation ofthe pump. Because the supply tube is formed of resilient material, thisvacuum will slightly reduce the diameter of the tube. A strain gagemounted against the outside wall of the tube senses the diameterreduction, and activates an occlusion alarm. Repeatedly placing thedisposable tubing accurately against such a strain gage is difficult andmakes such systems less reliable than would be desirable.

In a similar fashion, it is known to sense the diameter of the outlettube to monitor downstream occlusions, such as a blocked needle orobstructed tubing connection. Here, the prior art devices use staingages to sense the diameter increase in the outlet tube caused byincreased pressure which the blockage creates, so that an alarm may beactivated. These sensors are subject to the same weaknesses describedabove.

SUMMARY OF THE INVENTION

Briefly stated, the present invention is an improved occlusion sensingsystem for an ambulatory infusion device having a disposableadministration set. The occlusion sensor is relatively insensitive tomechanical misalignment of the disposable administration set in thepump, is inexpensive to manufacture and provides reliable, consistentprotection from both upstream (supply) and downstream (patient output)occlusions.

The present invention utilizes two pumping cams and two pumping camfollowers, which function such that, at any point in time, one of thetwo pumping cams is always pumping. The two pumping cams comprise aprimary pumping cam associated with an upstream segment of the deliverytube and a secondary pumping cam associated with a downstream segment ofthe delivery tube. The primary pumping cam is wider than the secondarypumping cam, so that it can displace sufficient fluid during its pumpingstroke to deliver fluid extent to the pump and at the same time deliverfluid to the section of the tubing beneath the secondary pumping cam toallow it to fill. The secondary pumping cam is narrower, since it onlyneeds to deliver fluid external to the pump. The present inventionadditionally utilizes pinching cams and pinching cam followers, whichopen and close the delivery tube to allow the pumping action to functionproperly. The pinching cams comprise an inlet pinching cam associatedwith the upstream segment of the tube and an outlet pinching camassociated with the downstream segment of the tube. Thus the pumping camfollowers, acted upon by the pumping cams, control the rate of fluidflow, while the pinching cam followers acted upon by the pinching cams,operate as valves for the pump. Such a configuration allows one segmentof the delivery tube to fill with fluid while another segment of thedelivery tube is pumping, thus providing a continuous and uniform fluidflow.

In still another feature of the present invention the disposableadministration set of the infusion device is less prone to operatorloading errors. This is accomplished through a reduced number ofrequired operations and a reduction in the complexity of the operations.This is facilitated by providing channels extending along the length ofthe walls of a housing structure of the infusion device. These channelsslidingly receive the disposable administration set in a simple, singleinsertion step. Additionally, since the disposable administration setincludes the delivery tube retainer plate and cam followers, theposition of the delivery tube relative to the tubing retainer plate andcam followers is established in a manufacturing operation which can beclosely controlled. Assemblers are not under the stress of a clinicalsituation and they specialize in the proper assembly of the disposableadministration set. Good manufacturing procedures provide additionalchecking systems to insure that the tubing is properly loaded and thatthe administration set properly assembled. These practices are notpossible in a clinical environment.

The set loading and retaining channels allow precise positioning of thetubing, followers, and pressure plate without any adjustments orcomplicated, bulky, or expensive mechanisms. The disposableadministration set results in an overall fluid delivery system which issmall, lightweight, and ambulatory.

The disposable administration set includes a channel segment which isslightly narrower than the outside diameter of the tubing. Consequently,when the tubing is positioned within this channel at the time ofmanufacture, a narrow portion of the tube wall will be flattened againstthe wall of the channel of the administration set. This narrow portionforms a contact line with the channel wall having a highly predictableline width. A source of illumination is directed at the channel wall,and a photodetector is used to measure the width of this contact line.If pressure within the tube causes the tube's diameter to increase, thecontact line width will increase. Likewise, if a vacuum is drawn withinthe tube, so that the diameter of the tube decreases, the contact linewidth will decrease. In fact, the contact line may disappear altogetherif contact between the channel wall and the tube ceases.

This channel segment is placed between the two pinching cam followerlocations in the pump. Thus, when the upstream pinching cam pinches theupstream follower against the tube, and the downstream pinching camfollower is raised away from the tube, the tubing in this channelsegment is subjected to the output pressure of the pump. When thedownstream pinching cam pinches the downstream follower against thedelivery tube, and the upstream pinching cam follower is raised awayfrom the tube, the tubing in this channel segment is subjected to theinlet pressure or vacuum of the pump. By synchronizing the measurementof the contact line width with the rotation of the cam, both theupstream and downs pressure may be sensed. This permits a single sensorto monitor for both upstream (supply) and downstream (outlet to patient)occlusions. The use of a single sensing mechanism for both upstream anddownstream occlusion sensing simplifies the pump construction, reducesthe cost of the system, and increases overall reliability.

In order to measure the contact line width, a light source, such as alight emitting diode (LED) is positioned on the outside of the channelwall at the channel segment. The channel wall is transparent, and thelight from the LED thus illuminates the region of contact between thetubing and the channel segment wall. If the light is introduced at anangle relative to the plane of the channel segment wall, total internalreflection will occur at the channel segment wall when the tubing doesnot contact the wall, i.e., when the difference between the index ofrefraction of the channel wall and surrounding air is relatively high.When, however, the tubing contacts the channel wall, because the tubinghas a higher index of refraction than air, the difference between therefractive indexes of the wall and the tubing is such as to prohibittotal internal reflection at the channel wall.

A photodetector is placed at the channel wall, and directed toward thecontact line. When total internal reflection occurs, the detector isilluminated. When no total internal reflection occurs, the detector isnot illuminated. As the contact line width increases, the degree oftotal internal reflection is altered, and the amount of light at thephotodetector changes. By measuring the output from the photodetector,the pumping system can determine the extent of pressure or vacuum in thetube at the channel segment.

If, during a time when the upstream pinching cam releases the upstreamfollower from the tubing, the output of the photodetector increases,indicating increased total internal reflection caused by a narrowing ofthe contact line due to vacuum in the tubing, an upstream occlusionalarm is activated. Similarly, during a time when the upstream pinchingcam closes the upstream follower against the tubing, the output of thephotodetector decreases, indicating deceased total internal reflectioncaused by a widening of the contact line due to pressure in the tubing,a downstream occlusion alarm is activated.

This occlusion sensing system is simple, rugged, reliable andinexpensive. It permits a single sensor to measure both upstream anddownstream occlusions, without requiring precise alignment of theadministration set within the pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the present invention is illustrated in andby the following drawings in which like reference numerals indicate likeparts and in which:

FIG. 1 is a perspective, exploded view illustrating an infusion devicehaving a disposable administration set in accordance with the presentinvention.

FIG. 2 is a perspective view illustrating a disposable administrationset for use with the infusion device of FIG. 1.

FIG. 3 is a cross section view taken along the line 3--3 of FIG. 1.

FIG. 4 is a plan view illustrating the single-piece cam of theinvention.

FIG. 4a is a cross section view taken along the line a--a of FIG. 4illustrating the contour of the outlet or secondary or downstreampumping cam of the present invention.

FIG. 4b is a cross section view taken along the line b--b of FIG. 4illustrating the contour of the outlet pinching cam of the presentinvention.

FIG. 4c is a cross section view taken along the line c--c of FIG. 4illustrating the contour of the inlet or primary or upstream pumping camof the present invention.

FIG. 4d is a cross section view taken along the line d--d of the presentinvention illustrating the contour of the inlet pinching cam of thepresent invention.

FIG. 5 is a plan view illustrating a can follower and spacer assembly ofthe present invention.

FIG. 6 is a side elevation exploded view illustrating the cam followerand spacer assembly and the plate assembly.

FIG. 7 is a graphical representation of the cam radii versus the angleof cam rotation of the present invention.

FIG. 8 is a graphical representation of the tubing ID gap versus theangle of cam rotation of the present invention.

FIG. 9 is a plan view of an the tubing retainer plate of theadministration set of this invention, showing the optical path elementsfor the occlusion detection system.

FIG. 10 is a sectional view of the tubing retainer plate of FIG. 9,taken along line 10--10 of FIG. 9, along with a broken away portion ofthe infusion device body, showing the positional relationship of theretainer plate when the administration set is installed in the infusiondevice.

FIG. 11 is a sectional view of the tubing retainer plate of FIG. 9,taken along line 11--11 of FIG. 9, showing the positional relationshipof the tubing and the retainer plate when the administration set isinstalled in the infusion device, and neither the inlet nor the outlettubing is occluded.

FIG. 12 is a sectional view of the tubing retainer plate of FIG. 9,taken along line 11--11 of FIG. 9, identical to FIG. 11, but showing thepositional relationship of the tubing and the retainer plate when theadministration set is installed in the infusion device and the inlettubing is occluded.

FIG. 13 is a sectional view of the tubing retainer plate of FIG. 9,taken along line 11--11 of FIG. 9, identical to FIGS. 11 and 12, butshowing the positional relationship of the tubing and the retainer platewhen the administration set is installed in the infusion device and theoutlet tubing is occluded.

FIG. 14 is a sectional view of the tubing retainer plate of FIG. 9,taken along line 14--14 of FIG. 9, along with a broken away portion ofthe infusion device body and the adjacent wall of the tubing, showingthe positional relationship of the retainer plate and the occlusionsensors when the administration set is installed in the infusion device.

FIG. 15 is a broken-away schematic view showing the view of the tubingretainer plate at the photosensor of the occlusion sensing system.

FIG. 16 is a schematic view, similar to the view of FIG. 14,illustrating the light path when there is no occlusion, or when there isa downstream occlusion.

FIG. 17 is a schematic view, identical to FIG. 16, except that itillustrates the light path when there is an upstream occlusion.

FIG. 18 is a schematic view, identical to FIG. 16, except that itillustrates the light path when there is a bubble in the fluid in thetubing.

FIG. 19 is a schematic view, identical to FIG. 16, except that itillustrates the light path when there is a downstream occlusion and afluid leak in the system.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 illustrates the infusion device 10 of the present invention foradministering intravenous fluid at a consistent and uniform rate. Theinfusion device 10 is designed to be small, lightweight and ambulatory.The infusion device 10 includes a disposable administration set 12having a plurality of cam followers 42 which are displaced in apredetermined sequence when depressed by a pumping mechanism 64 tosqueeze a delivery tube 36 for dispensing fluid. In FIGS. 1 and 2, asimplified administration set 12, without provision for the occlusionsensor of the present invention, is shown, and will be used to explainthe operation of the device 10 by way of background.

The pumping mechanism 64 is driven by a commercially available motor 11(not shown). The disposable administration set 12 loads easily into thehousing structure 66 adjacent the pumping mechanism 64. Orienteddirectly above the housing structure 66 is an optional fluid reservoir60 which provides a continuous flow of fluid to the inlet of thedelivery tube 36 for dispensing and infusing fluid into a patient'sbody. Alternatively, the fluid delivery tube 36 may connect to anexternal reservoir (not shown), or the reservoir 60 may be located atother positions on the assembly.

The housing structure 66 comprises a rectangular chamber 67 surroundedby side walls 68 and a rear wall 69. The floor of the rectangularchamber 67 drops into a recess 70 towards the front end. The pumpingmechanism 64 is located within the recess 70. Extending throughout thelength and parallel to the base of each of the side walls 68 is a narrowchannel 72 having a lower shoulder 73. The disposable administration set12 slides within the channel 72. As best seen in FIG. 3, each of thechannels 72 includes a spring-biased ball assembly 75. The disposableadministration set 12, while being manually inserted into the channels72, depresses the spring assemblies 75. After insertion of the set 12,the spring assemblies on either side bias the disposable administrationset 12 against the shoulders 73 of the channels 72, holding thedisposable administration set 12 accurately in position. In operation,the disposable administration set 12 is manually loaded into theinfusion device 10 in a simple sliding operation. As the administrationset 12 slides into the infusion device, the cam followers 42 aregradually pushed against the delivery tube 36 by the pumping mechanism64.

FIGS. 2 and 6 illustrate the simplified disposable administration set 12without the occlusion sensing of the present invention. The disposableadministration set 12 is formed from rigid transparent plastic or thelike, and includes a tubing retainer plate assembly 14 which mayadvantageously be injection molded as a single piece.

The tubing retainer plate assembly 14 includes a tubing retainer plate16 having a flat tube-contacting surface and a cam follower retainer 20projecting normal to this surface at one end. The cam follower retainer20 terminates in a an overhanging latch 24 projecting substantiallyparallel to the retainer plate 16. The latch 24 serves as a lockingmechanism for holding the cam followers 42 in position, adjacent thetube 36 prior to insertion of the administration set 12 into the housing66. During insertion of the administration set 12 into the channels 72,some of the cam followers 42 are depressed by the pumping mechanism 64.Between pumping cycles of the various cams, the followers return to astandby position against the latch 24.

As best seen in FIGS. 2, 5 and 6 the disposable administration set 12further includes a cam follower and spacer assembly 40. In the preferredembodiment of the present invention the cam follower and spacer assembly40 may also be injection molded as a single piece independent of thetubing retainer plate 16. Alternatively, the cam follower and spacerassembly 40 may be molded as one piece with the tubing retainer plateassembly 14 provided that a hinge is molded to connect the cam followerand spacer assembly 40 to the tubing retainer plate assembly 14. The camfollower and spacer assembly 40 includes two gap correction spacers 44in the form of elongated extending finger-like projections which flankthe tubing retainer plate 16 on either side (as best seen in FIG. 2).Since the cam followers 42 are instrumental in controlling the amount offluid dispensed, the thickness of the cam followers 42 is a criticaldimension which directly effects the volume of the delivery tube 36. Theaccurate pinching of the delivery tube 36 is necessary to allow adesired flow of fluid through the available passage. However, due totypical molding process variations such accuracy may not be possible.The gap correction spacers 44 advantageously counteract these thicknessvariations. During the molding process, the thickness of both the camfollowers 42 and the gap spacers 44 will vary by the same amount,because they are formed in the same mold cavity. Thus, any moldingvariations, such as those due to mold temperature or pressure, willaffect both of these parts identically.

Referring to FIG. 3, it will be seen that, after insertion of theadministration set 12 into the housing 66, the dispensing tube 36 ispositioned immediately below the siring-biased retainer 75. Thespring-biased retainer 75 holds the administration set accurately inplace against the shoulders 73 (as best seen in FIG. 1) as describedearlier. The cam followers 42 are pushed against the tube 36 by aplurality of cams 85, one of which is shown in FIG. 3. Pumping isaccomplished, as will be described below, by squeezing the tube 36.

The gap correction spacer 44 rests between the plate 16 and the shoulder73 (as best seen in FIG. 1). Thus, if the spacer 44 is thicker thannormal, the plate 16 will be positioned further from the cam 85 thannormal. However, in this case, as explained above, the cam followers 42will also be thicker than normal offsetting the effect of the thickerspacer 44. It is advantageous, in accomplishing this self correction,that the thickness of the spacer 44 be the same as that of the activepart of the follower 42, so that they will vary identically inthickness.

The plurality of cam followers 42, as best seen in FIG. 5, includes aninlet pincher cam follower 43, a primary, upstream, inlet pumping camfollower 46, an outlet pincher cam follower 48, and a secondary,downstream, outlet pumping cam follower 50. Each of the cam followers 42are attached to the cam follower and spacer assembly 40 by flexible camfollower arms 54. Each of the cam followers 42 are displaced toward thedelivery tube 36 in a predetermined sequence. The inlet pincher camfollower 43 and the outlet pincher cam follower 48 deform the fluiddelivery tube 36 to close it off, and thus act as valves. The primarypumping cam follower 46 and the secondary pumping cam follower 50 pumpthe fluid through the delivery tube 36. The primary pumping cam follower46 which contacts he upstream segment of the delivery tube 36 isapproximately twice the width of the secondary pumping cam follower 50,and it thus squeezes twice the length of tubing. This facilitatesdisplacement of enough fluid during a pumping stroke for deliveringfluid external to the pump and at the same time delivering fluid to thedownstream segment of the fluid delivery tube 36, beneath the follower50, to allow it to fill. Thus, as the follower 46 is being advancedtoward the tube 36, the follower 50 is being withdrawn. The fluiddisplaced by the follower 46 fills the tube 36 as it is released by thefollower 50, and also supplies enough fluid to continue the outflow fromthe pump.

Referring now to FIG. 4, the pumping mechanism 64 which provides acontinuous and uniform flow will be described. The pumping mechanism 64comprises a cam assembly 84 and an axle shaft 86. In the preferredembodiment, the cam assembly 84 is preferably formed and machined from asingle piece of metal. Alternatively, the cam assembly 84 may be cast,and later machined. As shown, the assembly 84 includes a centralaperture 83 to accommodate an axle shaft 86. The shaft 86 may include aflat 86a to couple the shaft 86 to a motor. The axle shaft 86 rotateswithin bearings which are in turn mounted in two apertures formed withinthe walls 68 as best seen in FIG. 1. The axle shaft 86 driven by themotor provides rotation to the cam assembly 84. The cam followers 42 aredisplaced in a predetermined sequence, as described below, therebysqueezing the delivery tube 36 and dispensing a specified volume offluid.

The cam assembly 84 is specifically designed such that each incrementalangle of revolution displaces the same amount of fluid. The cam assembly84 includes the plurality of spaced cams 85. The plurality of spacedcams 85 include an inlet pincher cam 87, a primary, upstream, inletpumping cam 88, an outlet pincher cam 90 and a secondary, downstream,outlet pumping cam 92. The inlet pincher cam 87 and the primary pumpingcam 88 are operably associated with the inlet pincher cam follower 43and the primary pumping cam follower 46, respectively. Similarly, theoutlet pincher cam 90 and the secondary pumping cam 92 are likewiseoperably associated with the outlet pincher cam follower 48 and thesecondary pumping cam follower 50.

Referring to FIGS. 4b and 4d the inlet pincher cam 87 and the outletpincher cam 90 will be described. The inlet pincher cam 87 and outletpincher cam 90 operate as valves for the pumping action. The surfaces ofthe pincher cams 87, 90 are contoured such that between specifiedrotational positions either the upstream or the downstream segment ofthe tube 36 is pinched off to obstruct fluid flow.

Referring to FIGS. 4a and 4c, the primary pumping cam 88 and thesecondary pumping cam 92 include active pumping surfaces which areuniquely contoured so that the fluid delivery tube 36 is squeezed insuch a manner that a constant speed of rotation of the axle shaft 86results in a uniform or constant displacement of fluid volume from theappropriate segment of the fluid delivery tube 36. To accomplish thisresult, the primary pumping cam 88 and the secondary pumping cam 92surfaces are contoured based upon the following principles andcalculations.

The equation defining the volume of a cylindrical tube with 1representing the length and d the inside diameter is as follows:##EQU1##

The equation defining the volume of an elliptical tube with grepresenting the inside edge diameter or minor gap and L representingthe portion of the cam in contact with the cam follower is as follows:##EQU2##

Since the circumference of the tube 36 remains relatively constant whenthe tubing is deformed from a cylindrical shape into an elliptical shapeby the cam followers 42, the cylindrical circumference equals theelliptical circumference.

    C.sub.eli =C.sub.cyl

Additionally the circumference of a cylinder and an ellipse are definedas C_(cyl) =πd and C_(eli) =2×L+π×g, respectively.

Thus since the circumference remains constant throughout the deformationprocess of the delivery tube 36, the two circumferences may be equatedas follows:

    π×d=2×L+π×g

Solving for L

    L=(π×d-π×g)/2

and substituting for area

    area=g×L+π×g×g/4=g×(π×d-π×g)/2+π×g×g/4

    area=(.sup.π /2)×g×d-(.sup.π /4)×g×g

considering that g=d as the total area displaced and breaking that totalarea into 100 equal area increments

    total area=π×d×d/.sub.4

and the

    incremental area change=π×d×d/.sub.400

and then solving for the 100 g values corresponding to each of the 100incremental area increments

    area 1=(.sup.π /2)×g×d-(.sup.π /4)×g×g=π×d×d/.sub.400

and solving for g given the constant cylinder d value and letting

    K=π×d×d/400 for simplification

    and letting π/4=c for simplification 2×c×d×g-c×g×g-k=0

and solving for the second incremental area

    2×c×d×g-c×g×g-2×k=0

and calculating the remaining 98 equal area increments.

An incremental part of the cam rotation is selected for filling and theremaining part of the rotation will be for pumping. For example, if 180°is selected for pumping, then each incremental area change will occur in1.8° increments such that the g for the first incremental area willoccur at 1.8 degrees, the g for the second incremental area will occurat 3.6 degrees, etc. Finally, the g for the 100th area will occur at 180degrees. The cam radiuses at each increment can then be calculated bysubtracting the required g value from the displacement between thecenter of the cam to the face of the plate assembly minus the camfollower thickness minus 2 times the tubing wall thickness plus the gapspacer thickness.

Using this derivation, it is possible to generate the proper cam pumpingprofile for any combination of tube diameter, cam spacing, tube wallthickness, and cam-degrees of pumping rotation.

The relationship between the cam radius and the tubing gap isalgebraically proportional only when the cam radius in constant. As thecam radius changes, the effect of the approximately horizontal surfaceof the follower, contacting the changing cam surface makes it necessaryto take the phase and amplitude into consideration. For example, arapidly increasing cam surface results in a gap change that leads theactual radius change. Likewise, a rapidly decreasing cam radius resultsin a gap change that lags the actual radius change. The amount of changein phase is a function of a ratio of the beginning and ending cam radii.

The present invention utilizes approximate predicted phase changes basedon calculations, of the ratio of the beginning and ending cam radii,relative to the rotational positions of the cam. This effect is moresignificant in the case of the rapidly changing pincher cams which arecharacterized by transitioning phase changes of approximately 35degrees. Thus, once the cam profiles and approximate rotationalpositions of each cam are selected, the actual gaps are numericallycomputed as described. For each degree of rotation, each radius has avertical component which is computed by multiplying the actual radiuslength by the cosine of the angle that is formed by that radius relativeto a vertical line. The vertical line passes through the center of theaxle shaft and is approximately normal to the surface of the camfollower. The vertical component of each radius thus changes as the camrotates about its axis. Since the follower is formed to contact the camsurface in an approximately downward direction, for a particular degreeof rotation of the cam, the cam follower will contact the cam surface atthe radius which has the greatest positive vertical component. Theactual radius of contact at each degree of rotation is determined bynumerically computing the radius with the greatest vertical component ateach degree of rotation.

Referring to FIGS. 4 and 7 the operation of the cams 85 relative to thegap of the delivery tube 36 will be described. The cam assembly 84, asseen in FIG. 4, rotates about the axle shaft 86 and acts through the camfollowers upon the delivery tube 36 positioned directly beneath the camassembly 84. As best seen in FIG. 7, between the rotational positions 0degrees and 200 degrees the inlet pincher cam 87, indicated by a curvetrace 87a, forces the inlet cam follower 43 to pinch off the upstreamsegment of the tube 36 to prevent fluid flow back into the reservoir 60.While the upstream segment of the tube 36 is pinched off, the primarypumping cam 88 progresses through a gradual pumping stroke lasting from0 degrees to approximately 175 degrees, indicated by the curve 88a. Thisdisplaces the inlet pumping cam follower 46 against the tube 36 tosqueeze enough fluid to the downstream segment as well as external tothe pump to continue to provide a uniform and consistent flow while thetube 36 beneath the secondary pumping cam 92 is filling. This filling iscaused by a reduction in the diameter of the cam 92 through thisrotational segment, as shown by curve 92a.

Once the downstream segment of the tube has been filled with fluid (atapproximately the 180 degree rotation point), the outlet pincher cam 90closes and remains closed between the rotational angles 200 degrees to340 degrees, indicated by the curve 90a. This forces the outlet camfollower 48 to pinch off the downstream segment of the delivery tube 36.When the cam 90 pinches the tube 36 at approximately the 180 degreerotational position, the cam 87 rotates to a reduced diameter regionwhich extends between approximately 220 degrees and 340 degrees. Thisopens the tube 36 beneath the cam 87, as shown by curve 87a, to allowfluid to flow from the reservoir 60 to the portion of the tube 36 whichunderlies the cam 88, so that this tube portion may fill. This allowsthe upstream segment to fill in response to a gradual reduction in theradius of the cam 88, as shown by the curve 88a between 220 degrees and340 degrees. During this segment, the secondary pumping cam 92,indicated by the curve 92a, depresses the secondary cam follower 50against the tube 36 dispensing fluid external to the pump.

Referring to FIG. 8, the affect of the cams 85 on the tubing gap duringtheir rotational movement is shown. The curves of FIG. 8 are thussomewhat inversely proportional to the curves of FIG. 7, since anincrease in cam radii causes a decrease in the corresponding tube 36gap, taking into account the fact that the gap change leads the actualradius change. The upstream segment of the tube 36, indicated by thecurve 87b is completely pinched off between the rotational positions 340degrees and 200 degrees. The primary pumping cam 88, as described above,reduces the gap beneath it to expel fluid until it reaches a rotationalangle position of 175 degrees, as indicated by the curve 88b. The gap ofthe tube 36 beneath the cam 92 is gradually increased during thissegment between 0 degrees and 180 degrees, so that the tube 36 beneaththe secondary pumping cam 92 will slowly fill with fluid.

Once the downstream segment of the tube 36 has been filled, the outletpincher cam 90 causes the downstream segment to be pinched off asindicated by the curve 90b so that the secondary pumping cam 92 candeliver fluid external to the pump. The tubing gap beneath the cam 92varies as indicated by the curve 92b during the pumping stroke (175degrees to 360 degrees) of the secondary pumping cam 92.

Referring now to FIG. 9, the construction and operation of the occlusionsensing system of this invention will be described. FIG. 9 shows thetube-retaining surface, that is, the lower surface as viewed in FIG. 1,and the upper surface as viewed in FIG. 2, of the tubing retainer plate16 of the disposable administration set 12. This plate is transparent,and thus an occlusion sensing recess 100 can be seen through the plate16 in the view of FIG. 9, though this recess is located on the undersideof the plate 16 in this view.

An inlet tubing aperture 101 guides the inlet tubing from the medicationsource to the upper surface of the tubing retainer plate 16. In asimilar fashion, an outlet tubing aperture 103 guides this same tube 36from the surface of the tubing retainer plate 16 to the patient. Betweenthese two apertures 101, 103, the tubing is guided, under slighttension, across the upper surface of the plate 16 between a series ofstanchions. A first stanchion 105 and a last stanchion 119 form fulcrumsaround which the tubing is bent as it enters and exits the plate 16, sothat the tubing can extend straight across the face of the plate 16therebetween. Between the first stanchion 105 and a pair of opposedstanchions 107, 109, the surface of the plate 16 is raised byapproximately 0.020 inches in a small region 110. This region 110 isalso shown in FIG. 10, and is opposite the inlet pinching cam follower43, and the raised surface 110 assists in assuring that the tubing willbe completely pinched off by the cam follower 43.

Similarly, between a pair of stanchions 111, 113 and another pair 115,117, the surface of the plate 16 in a region 112 is raised by 0.020inches at a location opposite the pinching cam follower 48 for the samereason.

When the tubing is in place on the plate 16, it is held against theregions 110 and 112 by the opposed pinching cam followers 43, 48, whichare in turn held down by the latch 24 (FIG. 2).

Between the stanchions 107, 109 and the stanchions 111, 113, because thetubing is under slight tension, the tubing is actually suspended abovethe surface of the plate 16, unless held against that surface by thefollower 46.

At a location midway between the stanchions 107, 109 and 111, 113, onthe underside of the plate, as viewed in FIG. 9, and as shown in crosssection in FIG. 11, there is a specially formed recess 100 for theocclusion sensing system of this invention. It should be noted that thisposition of the recess 100 is significant, as it underlies a portion ofthe tube 36 which is beneath the follower 46, and is between thepinching followers 43 and 48. Because of this location, the tubinglocated above the recess 100 is in direct fluid communication with theupstream (supply) tubing when the pinching follower 43 is open, and thepinching follower 48 is closed. This occurs, as can be seen from FIGS. 7and 8, following the 200 degree position and up until the following 335degree position the cam assembly. (Note that curves 87a and 87b relateto the movement of the follower 43, while curves 90a and 90b relate tothe movement of the follower 48.) In addition, at this location, thetubing located above the recess 100 is in direct fluid communicationwith the downstream (outlet to patient) tubing when the pinchingfollower 43 is closed, and the pinching follower 48 is open. Thisoccurs, as can be seen from FIGS. 7 and 8, following the 335 degreeposition, and up until the following 200 degree position of the camassembly. As a consequence, it is possible with a single sensing systemto detect occlusions in both the upstream and downstream connections tothe infusion device.

FIGS. 7 and 8 demonstrate that the pumping follower 46 is in a fullyraised position following the 250 degree position, and up until the 360degree position (Illustrated by curves 88a and 88b). Thus, following the250 degree position and up until the 335 degree position, the follower46 is at its fit position away from the plate 16, and the tubing is atits maximum diameter and in communication with the upstream or supplyportion of the tubing. Similarly, following the 335 degree position, anduntil the 360 degree position, the follower 46 is at its furthestposition away from the plate 16, and the tubing is at its maximumdiameter and in communication with the downstream or patient portion ofthe tubing.

Referring now to FIGS. 11, 12 and 13, the condition of the tubingimmediately opposite the recess 100 and under various operatingconditions will be described. In each of these figures, the follower 46is shown at its raised position, that is, the position furthest awayfrom the plate, so that the tubing is at its maximum diameter. In FIG.11, the tubing is in its normal condition, that is, neither expandedfrom pressure nor contracted from vacuum within the tube 36. In thiscondition, between the 250 degree position and the 360 degree position,the tubing is held against the surface of the plate 16 by the follower46 so that a relatively narrow region 121 of the tube 36 is in contactwith the plate 16 opposite the recess 100. The follower 46 is held inposition by the latch 24, so that the extent of tube 36 contact with theplate 16 is predetermined.

FIG. 12 shows the condition of the tube 36 between the 250 degreeposition and the 335 degree position, when a vacuum is drawn within thetube 36. The outside diameter of the tube 36 is reduced by the vacuum sothat the tube 36 cannot fill the distance between the surface of theplate 16 and the follower 46. Because the tube 36 is under slighttension, and is stretched between the raised regions 110, 112 (FIG. 9),the tube 36 will lift away from the surface of the plate 16 under theseconditions, so that there will be no contact between the tube 36 and theplate 16 opposite the recess 100.

FIG. 13 shows the condition of the tube 36 between the 335 degreeposition and the 360 degree position, when the medication within thetube 36 is under pressure. The outside diameter of the tube 36 isincreased by the pressure so that the walls of the tube 36 flatten outagainst the surface of the plate 16 and the follower 46. This flatteningwill increase the width of the region 123 of contact between the tube 36and plate 16 opposite the recess 100.

As will be seen from the following description, the extent of contactbetween the tube 36 and plate 16 is used to sense occlusions within thetubing.

Referring now to FIG. 14, a greatly enlarged cross sectional view of theportion of FIG. 11 in the region of the recess 100 will be described.The recess 100 is actually a pair of recesses 100a and 100b which areformed to direct light toward the interface of the tubing and thesurface of the plate 16. If the angle of incidence of the light withthis interface, and the respective refractive indexes, and properlyselected, total internal reflection of the light will occur at theinterface when the tubing is separated from the plate 16, but will notoccur at the interface when the tubing is pressed against the plate 16.The existence or lack of total internal reflection is used to determinethe condition of the tubing, and thus the existence of occlusions.

More specifically, within the wall 125 of the reservoir (FIG. 1), alight emitter 127 and a light detector 129 are mounted at respectiveangles of (theta)A and (theta)B, with regard to a line normal to thesurface of the wall 125. The wall 125 is parallel to, and slightlyspaced from the plate 16 when the administration set 12 is installed inthe infusion device 10. The light emitter 127 is typically a LEDincluding a lens 131 which creates a light beam which diverges atapproximately 10 (degrees). Similarly, the light detector 129 typicallyincludes a focusing lens 133 suitable for focusing a 10 (degree)converging light beam onto a photodetector 134.

The recess 100b is wedge-shaped and includes a surface 135 formed as aconvex lens which is coaxial with the light emitter 127. This lens 135collimates the light from the emitter 127, and directs the light towardthe surface 137 of the plate 16. The surface 137 is adjacent the wall138 of the tubing. Light which is reflected from the surface 137 isfocused by a similar convex lens 139 formed in wedge-shaped recess 100a.This lens 139 is co-axial with the light detector 129, and focuses thereflected light through the lens 133 to the photodetector 134. If theillumination output from the LED 127 is constant, changes in the lightlevel detected by the photodetector indicate the amount of lightreflection at the surface 137.

FIG. 15 illustrates the view of the surface 137 of the plate 16 from thephotodetector 129. In this figure, the oval 141 represents the field ofview of the photodetector 129. This field of view includes a firstregion 143 in which the tube 36 is in contact with the surface 137 ofthe plate 16, and a second region 145 in which the tube 36 is not incontact with the surface 137. As described earlier, the region 143 willwiden as the fluid in the tube 36 is pressurized, so that a wider region123 (FIG. 13) of the tube 36 is pressed against the surface 137. Whenthe tubing is subjected to a vacuum, so that no contact occurs been theplate 16 and the tube 36 (FIG. 12), the region 143 will disappearaltogether from the field of view 141. As will be described more fullybelow, total internal reflection occurs within the region 145, whileabsorption of the light incident from the LED 127 occurs in the region143.

Referring now to FIGS. 16-20, the operation and construction of theocclusion detection system will be described Referring first to FIG. 16,which shows schematically the path of light from the LED 127 when thetube 36 is separated from the plate 16, a condition which will occur ifthere is an upstream occlusion, such as an empty supply receptacle or apinched tube between the receptacle and the pump. In this situation,total internal reflection of the incident light should occur at theplate 16/air interface. As will be seen from the following analysis, ifthe refractive indexes of the plate 16 and tube 36 are known, the anglesθ_(A) and θ_(B) may be derived, so that the LED 127, photodetector 124and recess 100 may be properly oriented. If the refractive index of theplate 16 is Mp, and the refractive index of air is Ma (1.00), theexpression for total internal reflection is Sin (Theta)a≧Ma/Mp. If Mp is1.55, as is the case for polycarbonate, the plastic used in thepreferred embodiment for the plate 16, then (Theta)a≧40.2 degrees forTotal Internal Reflection.

Referring now to FIG. 17, the path of light from the LED 127 is shownwhen the tube 36 is pressed against the plate 125, a condition whichwill occur at the center of the tube when there is no occlusion, andacross a wider region when there is a downstream occlusion whichincreases the fluid pressure in the tube 36. In this case, absorption ofthe light should occur at the plate 125/tube 36 interface. If therefractive index of the tube 36, Mf, is 1.40, which is the case forclear PVC, the plastic used in the preferred embodiment for the tube 36,total internal reflection will occur if Sin (Theta)a≧Mf/Mp, i.e, if(Theta)a is greater than 64 degrees. Thus, to assure light absorptionunder these conditions, (Theta)a must be less than 64 degrees.

From these calculations, it is clear that a range of (Theta)a anglesexists (40-64 degrees for the preferred embodiment) which will providetotal internal reflection of the light beam when the tube 36 isseparated from the plate 125, and absorption of the light beam when thetube 36 is pressed against the plate 125.

Referring now to FIG. 18, the condition in which the tube 36 is pressedagainst the plate 125, but in which an air bubble, rather than fluid, isin the tube 36, will be described. Assuming light absorption occurs atthe interface of the plate 125 and the tube 36, as explained above forthe situation where the tube 36 is against the plate 125, total internalreflection can still occur at the tube 36/bubble interface. Due to thepassage of the light twice through the tubing wall, and to the fact thatthe light is reflected off a cylindrical rather than a flat interface,an offset occurs between the direct optical path (shown in dashed lines)and the light path from the tube 36/bubble interface. Thus, light willbe reflected back to the photodetector 129, but this offset in the lightpath will misaligned the light from the photodetector 129, so that morelight will be detected than without the air bubble being present, butless light that if the tube 36 is separated from the plate 125.

From the above description of FIGS. 16, 17 and 18, it can be seen thatthe occlusion sensing system of this invention provides a mechanism fordetecting a vacuum or high pressure in the tube 36, and for detectingthe presence of a bubble in the tube 36. In order to utilize thissensing mechanism to measure both upstream and downstream occlusions, aswell as air bubbles in the medication stream, the electronicsynchronizing system shown in FIG. 19 is used. A motor 151 rotates thecam of the pump mechanism 153. An encoder 155 is attached to the shaftof the motor 151 to generate a pulse during each incremental revolutionof the motor 151. The output of the encoder 155 is accumulated in aphase counter 157 which converts the encoder output into an outputcorresponding to degrees of rotation of the motor 151. A zero phasedetector 158 is used to reset the output of the encoder 155 and phasecounter 157 each time the motor rotates to a zero position, such as thezero angle positions of FIGS. 8 and 9. Thus, the output of the phasecounter 157, in the preferred embodiment, is a signal, defining motorand cam position, calibrated in terms of degrees of rotation referencedto a zero position as shown in these figures.

A look-up table 159 is connected to the output of the phase counter 157,and provides a first output 160 to a comparator 161 indicative ofwhether the cam position is appropriate to measure occlusions. Asdescribed in detail earlier, following the 250 degree cam position andup until the 335 degree position, the tubing is at its maximum diameterand in communication with the upstream or supply portion of the tubing,permitting upstream occlusion sensing. Similarly, following the 335degree position, and until the 360 degree position, the tubing is at itsmaximum diameter and in communication with the downstream or patientportion of the tubing, permitting downstream occlusion sensing. Thus, ata preselected angular position of the cam, such as the 300 degreeposition, an enable signal is sent from the comparator 161. At the sametime, a second output 162 from the look up table 159 indicates that anupstream occlusion is to be measured. In response to the second output160, a reference value selector 163 selects from a memory 165 thehighest appropriate photodetector output level from the photodetector129 in the absence of an upstream occlusion, i.e., when total internalreflection is not occurring throughout the width of the tube 36 andprovides this reference value to the comparator 161. If the output fromthe photodetector 129, converted in an A/D converter 167, is above thishighest appropriate output level, the comparator 161 issues an alarm,indicating that an upstream occlusion has occurred.

Similarly, at a preselected angular position of the cam, such as the 345degree position, an enable signal is sent from the comparator 161. Atthe same time, a second output from the look up table 159 indicates thata downstream occlusion is to be measured. In response to this output, areference value selector 163 selects from a memory 165 the lowestappropriate photodetector output level from the photodetector 129 in theabsence of a downstream occlusion, i.e., when light absorption is notoccurring throughout the majority of the width of the tube 36 andprovides this reference value to the comparator 161. If the output fromthe photodetector 129, converted in an A/D converter 167, is below thislowest appropriate output level, the comparator 161 issues an alarm,indicating that a downstream occlusion has occurred.

In addition, at this same 345 degree position, another output from thereference value selector 163 selects from the memory 165 the highestappropriate photodetector output level from the photodetector 129 in theabsence of an air bubble in the tubing and provides it to the comparator161, i.e., when total internal reflection is not occurring at the insidediameter of the tubing. If the output from the photodetector 129converted in the A/D convertor 167 is above this highest appropriatelevel, the comparator 161 issues an alarm, indicating that a bubbleexists within the medication.

Although this invention is described in terms of certain preferredembodiments, other embodiments that are apparent to those of ordinaryskill in the art are also within the scope of this invention.Accordingly, the scope of the invention is intended to be defined onlyby the claims which follow.

What is claimed is:
 1. A system for detecting deviations in the flow offluid through a flexible tube, the flexible tube providing fluidcommunication between a fluid source and a patient, the systemcomprising:a transparent plate in contact with the flexible tube; alight source configured to project light onto the transparent plate inthe direction of the flexible tube; and an optical sensor disposed suchthat it is directed at the transparent plate and the tube and isconfigured to measure reflected light; and wherein said transparentplate mounts the flexible tube such that when the flexible tube is in anormal flow condition, it is in contact with the transparent plate andwhen the flexible tube is exposed to an upstream occlusion condition,the tube has decreased contact with the transparent plate.
 2. The systemof claim 1 further comprising:an infusion pump which provides the flowof fluid through the tube.
 3. The system of claim 2 wherein the infusionpump has a housing which holds the transparent plate, the light sourceand the optical sensor.
 4. The system of claim 1 wherein the transparentplate mounts the flexible tube such that the flexible tube has a firstlevel of contact with the transparent plate when under a normalcondition at which the tube experiences pressure exerted by the flow offluid through the tube and a second level of contact with thetransparent plate when under an expanded state at which the tubeexperiences increased pressure caused by a downstream blockage of theflow, wherein the second level of contact with the transparent platewhen in the expanded state is a greater level of contact with thetransparent plate.
 5. The system of claim 1 wherein the transparentplate has an index of refraction which differs from the index ofrefraction of the flexible tube, such that increased contact between thetube and the transparent plate cause a decrease in the amount of lightreflected in a critical angle.
 6. The system of claim 5 wherein theoptical sensor is positioned to measure the amount of light reflected atthe critical angle.
 7. A system for detecting deviations in the flow offluid through a flexible tube, the flexible tube providing fluidcommunication between a fluid source and a patient, the systemcomprising:a transparent plate in contact with the flexible tube; alight source configured to project light onto the transparent plate inthe direction of the flexible tube; an optical sensor disposed such thatit is directed at the transparent plate and the tube and is configuredto measure reflected light; wherein the transparent plate has s firstsurface and a second surface, the second surface having a first recesswhich forms a lens configured to direct light emitted form the lightsource onto the first surface, and a second recess which forms a lensconfigured to direct light reflected from the first surface into theoptical sensor; and means for determining whether the measurementsreceived from the optical sensor indicate either an upstream ordownstream blockage in the flow through the tube.
 8. The system fordetecting deviations in the flow of fluid through a flexible tube, theflexible tube providing fluid communication between a fluid source and apatient, the system comprising:a transparent plate in contact with theflexible tube; a light source configured to project light onto thetransparent plate in the direction of the flexible tube; an opticalsensor disposed such that it is directed at the transparent plate andthe tube and is configured to measure reflected light; and means fordetermining whether the measurements received from the optical sensorindicate either an upstream or downstream blockage in the flow throughthe tube, wherein the determining means is capable of distinguishingbetween upstream occlusions and downstream occlusions.
 9. The system ofclaim 1 wherein the determining means is further capable of identifyingan air bubble in the flexible tube.
 10. The system for detectingdeviations in the flow of fluid through a flexible tube, the flexibletube providing fluid communication between a fluid source and a patient,the system comprising:a transparent plate in contact with the flexibletube and providing a mounting of the flexible tube wherein the flexibletube has a reference state when under the pressure exerted by thedesired rate of flow and a contracted state when under a vacuum exertedby an upstream blockage of the flow, wherein the contracted state hasdecreased contact with the transparent plate; a light source configuredto project light onto the transparent plate in the direction of theflexible tube; an optical sensor disposed such that it is directed atthe transparent plate and the tube and is configured to measurereflected light; and means for determining whether the measurementsreceived from the optical sensor indicate either an upstream ordownstream blockage in the flow through the tube.
 11. A system fordetecting deviations in the flow of fluid through a flexible tube, theflexible tube providing fluid communication between a fluid source and apatient, the system comprising:a transparent plate mounting the flexibletube at a first surface of the transparent plate, the plate mounting thetube such that the tube has a first level of contact with the firstsurface when in a normal condition during which fluid is flowing throughthe tube, a second level of contact with the first surface which isgreater than the first level of contact when there exists a downstreamblockage of the fluid, and no contact with the first surface when thereexists an upstream blockage of the fluid; a light source disposed forprojecting light onto a second surface of the plate in the direction ofthe first surface and the mounted tube, the second surface spaced fromthe first surface; an optical sensor disposed such that it is directedat the second surface of the transparent plate and at the first surfaceand the tube and is configured to measure reflected light; and means fordetermining whether measurements of reflected light received from theoptical sensor indicate an upstream blockage in flow through the tube ora downstream blockage.
 12. The system of claim 11 wherein the means fordetermining includes an electronic synchronizer.
 13. The system of claim12 wherein the electronic synchronizer further comprises:an analog todigital signal converter connected to the optical sensor; a set ofreference values stored electronically; and a comparator which receivesdigital signals from the signal converter and receives the storedreference values.
 14. The system of claim 11 further comprising:an alarmconfigured to activate in response to adverse indications from the meansfor determining.
 15. The system of claim 11 wherein the second surfaceof the transparent plate has a first recess which forms a lensconfigured to direct light emitted from the light source onto the firstsurface, and the second surface of the transparent plate has a secondrecess which forms a lens configured to direct light reflected from thefirst surface into the optical sensor.
 16. A system for detectingdeviations in the flow of fluid through a flexible tube, the flexibletube providing fluid communication between a fluid source and a patient,the system comprising:a transparent plate in contact with the tube; alight source for projecting light onto the plate; and an optical sensordirected at the transparent plate for measuring reflected light; whereinthe said plate having a first recess at which the light source isdirected and a second recess at which the optical sensor is directed,each recess having a lens for directing light.
 17. A system fordetecting blockages in the flow through a tube comprising:a flexibletube providing fluid communication between a fluid source and a patient,said tube defining a first diameter under a reference state due to auniform rate of flow through the tube; a transparent plate in contactwith the tube while the tube is in the reference state; and a lightsource configured to project light onto the transparent plate; and anoptical sensor configured to measure the light reflected from thetransparent plate.
 18. The system of claim 17 further comprising:anelectronic comparator configured to receive signals from the opticalsensor and determine whether the tube has deviated from the referencestate.
 19. The system of claim 18 wherein the electronic comparatordetermines whether the tube is in an expanded state due to a downstreamblockage or a contracted state due to an upstream blockage.
 20. Thesystem of claim 18 wherein the electronic comparator further determinesthe presence of an air bubble in the tube.